An optical communications module is a module having one or more transmit (TX) channels, one or more receive (RX) channels, or both. An optical transceiver module is an optical communications module that has one or more TX channels and one or more RX channels in the TX and RX portions, respectively, of the transceiver module. The TX portion comprises components for transmitting data in the form of modulated optical signals over one or more optical waveguides, which are typically optical fibers. The TX portion includes at least one laser driver circuit and at least one laser diode. The laser driver circuit outputs electrical signals to the laser diode to modulate it. When the laser diode is modulated, it outputs optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system of the transceiver module focuses the optical signals produced by the laser diode into the end of a respective transmit optical fiber held within a connector that mates with the transceiver module. An optical receiver module is an optical communications module that has the RX portion, but does not have the TX portion. An optical transmitter module is an optical communications module that has the TX portion, but does not have the RX portion.
Optical communications modules typically include one or more integrated circuits (ICs) for controlling the operations of the module. For example, an optical transmitter module typically also includes a controller IC that controls the laser driver circuit and other operations of the module. An optical receiver module typically includes a receiver IC that processes the signals received over the optical fiber to recover the data, as well as other operations of the module. An optical transceiver module typically includes a controller IC and a receiver IC.
Optical communications modules are often mounted on host circuit boards by sliding the modules into metal cages that are mounted on the host circuit boards. The cage not only supports the module mechanically, but also functions as an electromagnetic interference (EMI) shielding apparatus. In order to adequately perform the EMI shielding function, the cage must surround the module entirely except for small openings. Due to the module being surrounded by the cage, it is difficult to dissipate heat generated by the module. The heat dissipation problem makes the cage unsuitable for use with high-power optical communications modules and parallel optical communications modules that have multiple TX and/or RX channels and associated circuitry. In addition, the sides of the cage add to the total width of the optical communications system and reduce the number of optical communications system that can be mounted in a limited space on the circuit board. Furthermore, when such cages are used, the back side of the host circuit board is left unused for cooling.
It is known to use guide rail systems that do not require cages for mounting optical communications modules on a host circuit board. However, most, if not all, of the known guide rail systems have side walls or latch systems that protrude to the sides of the module. Similar to cages, these side walls and latch systems add to the total width of the optical communications system and therefore prevent high-density deployment of the optical communications systems. In addition, there is no back-side cooling capability in these systems.
Accordingly, a need exists for a guide rail system that accommodates high-density mounting of optical communications modules on a host circuit board while also providing adequate heat dissipation.